(1) Field of the Invention
This invention relates to the field of carburetor systems for internal combustion engines designed to operate with constant fuel to air ratios under a given set of conditions.
(2) Discussion of the Prior Art
Although significant progress in pollution abatement and improved efficiency of the internal combustion engine has been achieved by the use of recently developed dispersion enhanced, computer controlled carburetor systems, a decrease in engine performance under certain operating conditions such as start-up and acceleration has sometimes resulted. More particularly, the carburetor system disclosed in application Ser. No. 293,377 filed Sept. 29, 1972, entitled COMPUTER CNTROLLED SONIC FUEL SYSTEM, now U.S. Pat. No. 3,893,434, is capable of significantly improved pollution abatement and fuel economy over conventional carburetor systems by permitting the use of extremely lean fuel/air ratios. However, the use of such lean fuel/air ratios creates poor starting characteristics especially when the engine is cold since fuel at low temperature is not as easily vaporized and the air is more dense at a given pressure requiring the ratio of fuel to volume of air to be increased. Yet another problem which tends to impede the success of pollution abatement by modification of conventional carburetors is poor entrainment of fuel particles at engine start-up or idle. Poor entrainment and poor distribution occur at low speed because the particles of fuel are normally at least eight times heavier than air and tend to collect on the walls of the carburetor and intake manifold when the airstream is passing therethrough at a low velocity. This problem is compounded during start-up because the fuel which collects on the carburetor and intake manifold walls does not vaporize as is the case when the engine heat has had time to raise the temperature of these wall surfaces.
Even after warm-up the use of very lean fuel/air ratios may result in poor acceleration characteristics and the development of oxides of nitrogen when sufficient additional fuel is provided to obtain the desired acceleration characteristics.